Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 4, 2012
Publication Date: October 1, 2012
Citation: Shaner, D.L. 2012. Comparison of the Dissipation of Sulfentrazone and Pendimethalin in the Field. Weed Technology 26:633-637 Interpretive Summary: Pendimethalin and sulfentrazone are two soil-applied herbicides used to control weeds in sunflowers. It is important to know how these herbicides dissipate and move in the soil in order to use them safely and correctly. This study was done to determine the effect of irrigation/precipitation on the movement and dissipation of pendimethalin and sulfentrazone in the field in 2008 and 2010. Pendimethalin binds very tightly to the soil and thus, over 90% of the herbicide remained in the top 7.5 cm of the soil profile. The rate of dissipation of pendimethalin was not affected by the amount of irrigation/precipitation received in the plots in either year. The time it took for 50% of the herbicide to dissipate (DT50) was approximately 40 days. Sulfentrazone, on the other hand, does not bind to tightly to the soil and leached throughout the top 30 cm of the soil profile. The amount of leaching depended on the timing and amount of water received. The DT50 for sulfentrazone also depended on the year. In 2008 the DT50 was 30 days whereas in 2010 the DT50 was 14 days. The results from this study show that there is a much greater potential for sulfentrazone to leach in the soil compared to pendimethalin and the DT50 for sulfentrazone can vary from year to year.
Technical Abstract: Pendimethalin and sulfentrazone are applied PRE in sunflowers to control many grasses and broadleaf weeds. These herbicides have quite different physical-chemical properties. Pendimethalin has a high Koc (17,200 ml g-1) with a low leaching potential whereas sulfentrazone has a low Koc (43 ml g-1) with a high leaching potential. A two year study was conducted to determine the dissipation and leaching of these two herbicides applied to a loamy sand soil. Pendimethalin dissipated in two phases, an initial rapid loss between application and three to five d after application (DAT) and then a slower rate of dissipation. The first, rapid phase was likely due to volatilization of the herbicide from the soil surface. Pendimethalin dissipated at the same rate for the slower phase in 2008 and 2010 (half-life (DT50) 43, and 39 in 2008, and 2010, respectively). The dissipation of sulfentrazone, unlike pendimethalin, was not biphasic. However, the DT50 for sulfentrazone was different between the two years (30 d and 14 d in 2008 and 2010, respectively). Pendimethalin remained primarily in the top 7.5 cm of the soil column whereas sulfentrazone leached down to at least 30 cm. The amount of leaching of sulfentrazone depended on the timing of irrigation/precipitation after application. The more rapid dissipation of sulfentrazone in the top 30 cm of the soil column in 2010 could have been partially due to the herbicide leaching below the 30 cm depth that was sampled.